The present invention relates to a device that includes a hydraulic motor which is operable to drive an output shaft, and a brake assembly which is engageable to hold the output shaft against rotation when the motor is in an inactive condition.
A known hydraulic device having a motor which drives an output shaft and a brake assembly which holds the output shaft against rotation when the motor is in an inactive condition is described in U.S. Pat. No. 3,960,470, entitled xe2x80x9cHydraulic Motor Brakexe2x80x9d. This known hydraulic device includes a motor of the gerotor gear type. During operation of the motor, a rotor orbits and rotates relative to a stator. A portion of a wobble or drive shaft is connected with the rotor for orbital and rotational movement with the rotor. An outer end portion of the drive shaft is telescopically received in a hollow inner end portion of an output shaft. During operation of the motor, the drive shaft rotates the output shaft.
The hydraulic device of the aforementioned U.S. Pat. No. 3,960,470 includes a brake assembly which is connected to a portion of the drive or wobble shaft and is disposed on a side of the motor opposite from the output shaft. The brake assembly includes movable disks which rotate and orbit with the drive shaft during operation of the hydraulic motor and stationary disks which are interleaved with the movable disks. When the motor is in an inactive condition, the movable and stationary brake disks are pressed together to hold the drive shaft and, therefore, the output shaft against rotation. When the motor is to be operated, the brake assembly is released to enable the drive shaft to rotate and orbit. The housing for this devices includes a long cylindrical casing that encloses a complex arrangement of components for the motor and brake assembly of this construction.
A similar hydraulic device is described in U.S. Pat. No. 4,981,423, entitled xe2x80x9cHydraulic Motor With Wobble-Stick And Brake Assemblyxe2x80x9d. In this device, the outer end of the drive shaft is also received in a hollow end portion of the output shaft. A fluid flow passage is provided through the hollow end portion of the output shaft to the motor. A seal engages the outer surface on the hollow end portion of the output shaft to block hydraulic fluid flow between the motor and the brake assembly while allowing hydraulic fluid flow through the passage during operation of the motor. The housing for the device includes three separate components, a cup-shaped body portion, a cup-shaped intermediate portion and a cover portion to contain the brake disks, compression springs and piston of the brake assembly.
While the above hydraulic devices have certain advantages, it is believed that there is a demand for a hydraulic device which is even easier to manufacture and assemble than the know hydraulic devices, is more compact, provides less chance of leakage, and has consistent, reliable operation even at high pressures. High pressure operation can sometimes cause internal components to cock or bind during operation, which is undesirable in many circumstances.
The present invention provides a hydraulic device that is easy to manufacture and assemble, is compact, minimizes the chance of leakage, and has consistent, reliable operation even at high pressures.
According to the present invention, the hydraulic device includes a housing enclosing a hydraulic motor and a brake assembly. The motor is located at one (rear) end of the housing and includes a stator and a rotor having cooperating teeth which define fluid pockets. The rotor rotates and orbits relative to the stator when hydraulic fluid is directed to the pockets. An inner end portion of a wobble or drive shaft is connected with the rotor for rotational and orbital movement with the rotor relative to the stator. An outer end portion of the wobble shaft is received in a hollow inner end portion of a rotatable output shaft. The output shaft extends axially through the housing and outwardly from the other end of the housing, and rotates upon rotation and orbital movement of the rotor.
The brake assembly is connected with the output shaft at the other (front) end of the housing opposite from the motor. Prior to initiation of operation of the motor, the brake assembly holds the output shaft against rotation. Upon initiation of operation of the motor, the brake assembly is operated to a disengaged condition to allow the output shaft to be freely rotated by the hydraulic motor.
The brake assembly includes a plurality of brake disks interleaved in face-to-face relation with one another, with at least some of the disks being fixed to the output shaft for rotation therewith, and other of the brake disks being fixed to the housing. An annular actuator piston surrounds the output shaft and is axially moveable with respect thereto. A series of compression springs are normally biased against a rear annular surface of the piston to urge the piston forwardly against the brake disks to cause the brake disks to brake the output shaft. An annular fluid pressure cavity defined by a front surface of the piston, axially-opposite from the rear surface, moves the piston rearwardly away from the brake disks when fluid above the force of the spring enters the cavity. The springs are provided toward the motor (rear) end of the housing, the brake disks are provided at the opposite (front) end of the housing, and the piston is disposed axially between the springs and the brake disks.
The actuator piston for the brake assembly includes an annular, radially-extending, preferably flat stop surface at the rear end of the piston. The housing includes a corresponding annular, radially-extending, preferably flat stop surface in opposing relation to the piston stop surface. The stop surface of the piston engages the stop surface of the housing along at least the inner and outer diameters of the piston prior to maximum compression of the spring. The piston is prevented from cocking or binding at the end of its stroke, and possibly causing seizure or fatigue failure of the piston, particularly during high-pressure operation.
The housing for the hydraulic device includes a unitary, one-piece housing cover at the forward end of the housing having a central opening for the output shaft. The housing cover has a cup-shape and receives and at least partially encloses the brake disks and the annular piston to allow pre-assembly of these components. The housing further includes a unitary, one-piece housing body having a series of axially-extending cylindrical cavities to receive the compression springs. The cup-shaped end cover and housing body sealingly enclose the brake disks, annular piston and compression springs therebetween. The two-piece housing (cover and body) provides a compact hydraulic device that is easy to manufacture and assemble.
A thrust bearing is disposed adjacent the inner end of the output shaft in the motor pressure zone. The thrust bearing at least partially axially supports the inner end portion of said output shaft for rotation relative to the housing, and is continuously lubricated by the fluid supplied to the motor. An annular seal is provided between the thrust bearing and the brake assembly to block fluid flow between the hydraulic motor and the brake assembly.
Further features of the present invention will become apparent to those skilled in the art upon reviewing the following specification and attached drawings.